A starter head for an internal combustion engine conventionally comprises a starter pinion which is arranged to be displaced axially on a motor shaft until it comes into engagement with a toothed crown fitted around the engine flywheel. A free wheel and a drive sleeve are associated with the starter pinion, to which they are secured by means of a fastening shroud.
The drive sleeve has at one of its ends a set of helical splines, which cooperate with helical splines formed on the engine shaft so as to couple the starter head assembly to the motor shaft, for rotation together with the latter. Displacement of the starter head from its rest position to its working position, in which the starter pinion is meshed with the toothed crown on the flywheel, is effected by pivoting action of an actuating lever which is controlled in a known manner by an electro-magnet which also constitutes a contactor.
When the engine has started, the starter head must be returned to its rest position. This movement is effected by pivoting of the actuating lever in the reverse direction, this being initiated by the return spring of the contactor and the cooperation of the said lever with a return device which is secured to the starter head. Most commonly, this return device is arranged on the drive sleeve of the starter head.
In the case where the drive sleeve is made by matching a metal bar, the return device comprises an integral sleeve, so that the assembly is in monobloc form, as, for instance, is disclosed in the specification of French published patent application No. FR 2 145 116A. Although an arrangement of this kind is satisfactory in terms of mechanical reliability, its manufacture necessitates additional machining operations, which increase the cost of the starter as a whole in a somewhat prohibitive manner.
Alternatively, the drive sleeve may be made by extrusion, in which case the return device has to be mounted on it, and must thus consist of components which are separate from the drive sleeve itself.
In order to fulfil this function, proposals have been put forward to make the return device in the form of a movable pulley. This movable pulley may comprise two pressed rings which are separated by a spacing ring, one of the pressed rings being held against translational movement by a cotter pin. Such an arrangement, which is disclosed for example in the specification of French published patent application No. FR 2 064 768A, not only calls for a substantial number of components, but is a complex assembly which is not suitable for the kind of quality production that prevails in the automotive industry.
It has also been proposed to replace the movable pulley arrangement with an immovable pulley, which is prevented by a cotter pin from performing any translational movement. This arrangement is disclosed in the specification of French published patent application No. FR 2 615 568A. Such an arrangement calls for a stepped groove to be machined in the drive sleeve. Apart from the additional cost involved in machining and assembly, the ring is unable to be prevented from rotating, and this inevitably gives rise to noise problems while the starter is operating.
Replacement of the ring and its associated cotter pin, by means of a ring which cannot be lost in a groove, in no way resolves the noise problems mentioned above. Such a ring is initially of a conical shape, and is then fitted in the groove, in which it is realigned so that it becomes flat. To prevent it from escaping, this necessitates heat treatment of the ring with the drive sleeve.